Re: ums-realtek driver uses stack memory for DMA

[Josh Boyer <jwboyer@redhat.com>]

On Tue, Aug 02, 2011 at 08:41:17AM -0400, Josh Boyer wrote:
> On Mon, Aug 01, 2011 at 11:04:11PM -0600, Adam Cozzette wrote:
> > On Mon, Aug 01, 2011 at 05:09:06PM -0400, Josh Boyer wrote:
> > > Hello,
> > > 
> > > We have a report that the ums-realtek driver is generating a backtrace
> > > due to using stack variables for DMA buffers.  The backtrace is below
> > > and you can view the bug report here:
> > > https://bugzilla.redhat.com/show_bug.cgi?id=720054
> > > 
> > > Looking through the code, it seems that every call to rts51x_read_mem,
> > > rts51x_write_mem, and rts51x_read_status passes a stack variable to
> > > rts51x_bulk_transport, which then calls usb_stor_bulk_transfer_buf with
> > > this and generates the backtrace.  It is my understanding that the
> > > driver should be passing variables that are not on the stack and have
> > > been allocated with memory that will be suitable for the DMA api (e.g.
> > > kmalloc).
> > > 
> > > Was this missed during the initial review and is anyone working on
> > > adapting the driver to be compliant?
> > 
> > Could you try out this patch if it looks ok to you? I have not tested it because
> > unfortunately I don't have the hardware. Right now it generates some compile
> > warnings like this one:
> > 
> > drivers/usb/storage/realtek_cr.c:419:40: warning: ‘buf[0]’ may be used uninitialized in this function [-Wuninitialized]
> > 
> > It think they are harmless but I didn't see an obvious way to get rid of them,
> > so if you have any suggestions I would be glad to hear them.
> > 
> > This patch changed rts51x_read_mem, rts51x_write_mem, and rts51x_read_status to
> > allocate temporary buffers with kmalloc. This way stack addresses are not used
> > for DMA when these functions call rts51x_bulk_transport.
> > 
> > Signed-off-by: Adam Cozzette <acozzette@cs.hmc.edu>
> 
> This looks pretty good.  I backported it to 3.0 and will do a scratch
> build for the bug reporter to test with.

We've included this patch for a while now.  I think it should get queued
up in mainline.

josh